Typically, when two rotatable members are mutually connected to transmit mutual rotations by, for instance, extending a rotary shaft or connecting another rotary component to an end of a rotary shaft, various types of rotation transmitters are used. Such a rotation transmitter is also called a shaft coupling, joint, or coupling.
Such a rotation transmitter is required to mutually transmit rotational forces and rotation angle positions between the two connected rotary members as a basic function. Further, when the rotation transmitter is applied to a highly accurate rotation mechanism such as a roundness measuring device, the rotation transmitter is required to allow for an angular misalignment, a parallel misalignment and an axial displacement of the rotation axes of the connected members.
In the roundness measuring device, a rotation accuracy of a table on which a workpiece is placed is enhanced in order to measure roundness of an outer periphery of the workpiece at a high accuracy. In order to rotate the table, a driving shaft for transmitting a rotational force is connected to the table.
Herein, there is inevitably an angular misalignment (an angle of deviation, an inclination of each of central rotation axes), a parallel misalignment (eccentricity, misalignment in an intersecting direction of the central rotation axes) and an axial displacement (deviation of the central rotation axes in an axial direction, axial advance and retraction) between the table and the driving shaft.
When such angular misalignment, parallel misalignment and axial displacement of the rotation axes are directly transmitted from the driving shaft to the table, the rotation accuracy of the table is occasionally affected.
In order to solve the above problem, various rotation transmitters (a universal joint, flexible joint or flexible coupling) capable of reducing or absorbing the angular misalignment, parallel misalignment and axial displacement as described above have been conventionally proposed.
Patent Literature 1 (JP2010-203469A) discloses a so-called disc rotation transmitter, in which a pair of rotary shafts coaxially disposed are connected to each other with a disc member interposed therebetween and disposed in a direction orthogonal to the rotary shafts, thereby transmitting the rotation of the rotary shafts. The disc rotation transmitter allows for an angular misalignment and an axial displacement of the rotary shafts with use of deformation of the disc.
However, since an axial center of each of the rotary shafts is fixed to the disc member, it is difficult to adjust a parallel misalignment of the rotary shafts.
Patent Literature 2 (JP2008-208952A) discloses a so-called cross-joint rotation transmitter, in which a pair of a first rotary shaft and a second rotary shaft coaxially disposed are connected to each other by two pairs of connecting pins disposed in directions orthogonal to each of the first and second rotary shafts, one pair of the two pairs intersecting with the other pair of the two pairs, thereby transmitting the rotation of the rotary shafts. An angular misalignment of the rotary shafts is allowable by a rotation around at least one of the two pairs of connecting pins. A parallel misalignment of the rotary shafts is allowable by a displacement of each of the pins in its longitudinal direction.
However, since the rotary shafts cannot be displaced in an axial direction, it is difficult to adjust an axial misalignment of the rotary shafts.
Patent Literature 3 (JP Registered Utility Model No. 2512843) discloses a so-called Oldham rotation transmitter, in which two sets of slide structures, each set of which includes a convex portion and a concave groove extending in directions intersecting with rotary shafts, are combined in a manner to intersect with each other, thereby transmitting the rotation of the rotary shafts. The Oldham rotation transmitter allows for a parallel misalignment of the rotary shafts by a displacement of the slide structures in their longitudinal directions, allows for an angular misalignment of the rotary shafts by an angular displacement of the convex portions and the concave grooves of the slide structures, and further allows for an axial misalignment by an axial displacement of the convex portions and the concave grooves of the slide structures.
However, since the longitudinally slidable convex portions are respectively fitted in the longitudinally slidable concave portions in the Oldham rotation transmitter, a fitting clearance for assembly of the corresponding convex portion and concave groove, which also serves as a predetermined clearance for sliding, is required. Since the Oldham rotation transmitter has such a clearance, backlash occurs in the rotation transmission, inevitably resulting in adversely affecting the accuracy of the rotation angle positions.
In order to solve the problem of the Oldham rotation transmitter, the inventors of the present application propose a novel rotation transmitter (Patent Literature 4 (JP2014-34996A)).
The rotation transmitter of Patent Literature 4 has basic mutually-intersecting-slide structures of a typical Oldham rotation transmitter and further includes a mechanism of adjusting positions of sliders of the respective slide structures with respect to guide surfaces, thereby eliminating backlash during the operation of the rotation transmitter.
The inventors of the present application propose a novel rotation transmitter that is a combination of a disc rotation transmitter and a cross-joint rotation transmitter to solve various disadvantages (Patent Literature 5 (JP2014-34997A)).
The rotation transmitter of Patent Literature 5 has a cross-joint structure combined with a disc and is configured to adjust an axial misalignment, which is difficult to adjust in a cross-joint rotation transmitter, with use of elasticity of the disc.
With the above rotation transmitter of Patent Literature 4 or 5, all of the angular misalignment, the parallel misalignment, and the axial misalignment, which are difficult to adjust in a typical rotation transmitter, have been allowable.
However, even with the rotation transmitter of Patent Literature 4 or 5, the following disadvantages have occurred when a higher accuracy is required.
Specifically, in the rotation transmitter of Patent Literature 4, the parallel misalignment is smoothly adjusted using the mutually intersecting slide structures. However, the adjustment of the angular misalignment of the rotary shafts further requires a sliding guide using guide surfaces and the sliders while the adjustment of the axial misalignment only requires the sliding guide using the guide surfaces and the sliders. When such a sliding guide is used, the sliding guide transmits a friction force, which may adversely affect a highly accurate rotation transmission.
Moreover, in the rotation transmitter of Patent Literature 5, the angular misalignment and the parallel misalignment of the rotary shafts are smoothly adjusted using the cross-joint structures intersecting with each other. However, since the axial misalignment is adjusted solely using the elastic deformation of the disc, an elastic force is transmitted, which may adversely affect a highly accurate rotation transmission.